Comparing small mammal assemblages between communal and commercial rangelands within a region of the Succulent Karoo, South Africa

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Comparing small mammal assemblages between communal and commercial rangelands within a region of the Succulent Karoo, South Africa

Haveron, Sara Elizabeth

2008-12

The widespread ecological impacts of overgrazing by livestock within the Succulent
Karoo have received considerable attention. Literature shows communal and
commercial rangelands have been thoroughly studied, and vegetation responses have
been investigated in an attempt to understand the effects of overgrazing. Regarding
animal species, literature is in short supply. In a one-year study of small mammal
assemblages, the effect of the rangelands, and subsequently vegetation, on small
mammal assemblages was examined, as well as the effects on number of occupied,
unoccupied and collapsed burrows.
This study shows that vegetation composition differs between rangelands, with a
greater perennial shrub cover on the communal rangelands and a greater perennial
succulent cover on commercial rangelands, consequently creating different habitats
for animal assemblages. This study supports the notion of small mammal
composition relating to vegetation structure, with certain species being impacted by
heavy grazing. Four small mammal species were found in greater abundances on
commercial rangelands, with one being exclusive, while communal rangelands were
exclusively occupied by three nocturnal species. Diet and habitat requirements are the
most important factors regarding species occurrence. With small mammal species
composition differing between rangelands, and species richness not being affected by
rangeland type, this study illustrates that the disappearance of certain species may
arise without these different rangelands. This could result in reduced species richness,
and thus diversity being lost.
Regarding species present on both rangelands, no differences were observed in body
mass, body size or body condition. Despite no differences found in body condition,
calculating a body condition index is a good method for investigating how a species is
coping within an environment. The proportion and number of occupied and collapsed
burrows can be seen as a measure of trampling effect. It was expected for grazing
intensity, as well as vegetation changes, to affect the occurrence of such burrows.
This study showed differences between the communal and commercial rangelands as
negligible. As expected, numbers of burrowing small mammal species were
negatively correlated with numbers of collapsed burrows. However, a lack of
consistency deemed this result unimportant.
Results show that the effects of overgrazing on small mammal populations are
complex and require more attention if to be fully explained. This study provides
insights into the effects of land use on small mammals and burrow numbers, which
have implications for the conservation of these species within arid regions.